The purpose of this continuing study is to determine the prevalence and progression of gingivitis, epithelial attachment loss, and bone loss in a group of adolescents residing in the U.S. The original cross-sectional study population consisted of approximately 600 Navajos, ages 14-19 years. Twenty-four posterior interproximal sites were examined on each subject. Gingivitis was assessed using a modification of the G.I. Loss of attachment was assessed using Ramfjord's technique. Bone loss was diagnosed from standardized bitewing radiographs. Analyses indicated a high prevalence of disease: gingivitis (71%); attachment loss (89%); and bone loss (89%). The average number of sites in the mouth affected with the more advanced form of disease (attachment loss and bone loss) was also high: 32% of the sites had attachment loss, and 22% had bone loss.* A longitudinal study is in progress with the youngest subjects to investigate microbiologic, systemic and other factors that may contribute to the high prevalence of disease; 226 first and second year students were examined in February 1986, using the same clinical and radiographic techniques. In addition, subgingival plaque samples were obtained from mesiobuccal sites at all permanent molars and analyzed for A. actinomycetocomitans, B. Gingivalis and B. intermedius.